The upstate man charged in the cold-case slaying of the daughter of a former NYPD detective was released without bail Wednesday after a legal gaffe by local prosecutors.

Edward Holley, who was hit with murder charges last week in the 2003 death of 20-year-old Megan McDonald, will remain free for now because the Orange County District Attorney’s Office failed to present the case to a grand jury in time, a judge ruled.

“They never made out a case for even probable cause,” Holley’s defense attorney, Paul Weber, told The Post. “[Judge Peter Green] followed the law. He did what he had to do.”

Under state law, prosecutors have a strict timeline to try to secure an indictment against a defendant being held behind bars — who must be released if they blow the deadline.

Holley is still facing murder charges in the 20-year-old case. Should he be indicted by a grand jury, prosecutors could ask the judge to throw him back in jail or set bail.

“Our family is disappointed with today’s news regarding the release of Edward Holley,” McDonald’s family said in a statement Wednesday.

“Since Megan was brutally taken from us we have been advocating for the arrest of the person responsible for her murder,” they said. “After patiently waiting for over 20 years we are confident that the police have arrested the right person — Edward Holley.

“The process may not be easy or follow our preferred path,” the family said. “But we will not rest until justice is secured for Megan.”

John Beatty, the family’s attorney, added that while Holley’s release was “disheartening,” the family knew of it in advance and was “already aware of this phase of the criminal justice process.”

Orange County District Attorney David Hoovler said prosecutors just didn’t have time to get the case ready.

“Edward V. Holley was released from custody by operation of law as it is not feasible for any prosecutor to present a matter of this size and complexity — and obtain an indictment — within the six days required by New York State law,” the statement said. 

“To avoid any prejudice in the matter, the Orange County District Attorney’s Office will be referring future media inquiries concerning the case to the special district attorney,” it said.

Veteran attorney Julia Cornachio will take over as the special prosecutor. 

Holley, 42, is accused of killing McDonald on March 14, 2003 — with the case unsolved until last week.

McDonald, the 20-year-old daughter of former NYPD Detective Dennis McDonald, who died a year before she was killed, disappeared after she left a local party to seek out Holley — her estranged ex-boyfriend — to buy marijuana, state police said last week.

Interviews conducted by state police investigators led “to the inference that as a last resort the victim acquired or intended to acquire marijuana from Holley shorter after her last outgoing call at 12:20 a.m.” March 13, 2003, according to the complaint.

McDonald had just left a friend’s party to meet up with Holley, the complaint said. Then she disappeared.

Investigators determined that McDonald was killed while sitting in the driver’s seat of her 1991 Mercury Sable, with her body dumped along a dirt path on Bowser Road in Wallkill, police said.

On Wednesday, Holley was brought into court in a wheelchair and ordered freed.

“Based on the law, I’m required to release you, sir,” Green told Holley in Town of Wallkill Court, the Times Herald-Record reported.

Holley is due back in court on May 3.